IP-address (IP from the English Internet Protocol) - is a digital identifier, assigned to a device that operates in a public or local network based on TCP / IP protocol stack. Without it, the Internet or any internal IP network cannot exist.

Compare the IP address with a telephone number or home address - both point to an object. Just as a person calls a number, a computer calls another device with an IP address.

Let's analyze the structure of IP-addresses on the example of the first and most common Internet protocol IPv4.An IPv4 IP address has a 32-bit (4 bytes) structure. It is divided into 4 parts, each consisting of 8 bits (1 byte) and is called an octet. Each bit of an IP address is a binary digit.

An example of an address (IPv4) in binary form: 11000000.10101000.00110010.00000001.
Converting an octet from binary to decimal results in a single number with a value between 0 and 255.
IP address in decimal form: 192.168.50.1.

Devices distinguish parts of an IP address using a subnet mask, a 32-bit string divided into 4 octets, just like an IP address. When a connection is established, each octet of the IP address is mapped to an octet of the subnet mask.
The default subnet mask on a standard home network is 255.255.255.0.
In the example, the IP address mask is given in decimal representation and contains the numbers "255" and "0". The first identifies the network and the second identifies the destination host.

Class A. The highest bit in addresses of this format is always 0. The initial octet is responsible for identifying the network, allowing 127 unique networks. The remaining 3 octets are used to identify nodes, with a maximum of 17 million per network.

Class B. The first bits of the IP address are 10. The initial two octets refer to the network ID and the last two octets refer to the node ID. There may be 16384 networks, each supporting 65000 nodes.

Class C. The initial bits of the IP address are 110. The first three octets are responsible for the network identification and allow the creation of 2 million networks. The last octet is used to identify the nodes, the maximum number of which is 254 per network.

Class D. The IP address is recorded beginning with bits 1110. A network of this format uses a broadcast to send messages to multiple nodes.

Class E. IP addresses are reserved for future use. The first bits are always 11110. An IP address in a class-based network addressing architecture has two parts:
Network ID. Identifies the network containing the connected nodes.
Node ID. It's responsible for specifying a node: server, router or any other TCP/IP device.

Important! Because of limited resources of addresses IPv4, nowadays class addressing is almost ceased to be used. It has been replaced by the technology of Classless Inter-Domain Routing (CIDR). Classless Inter-Domain Routing uses the IPv4 address range more sparingly because it does not strictly bind subnet masks to subnet addresses.

Any network with IP addressing is based on TCP/IP, a model that includes a stack of protocols used to transmit data over the network. The basic protocols are TCP and IP, but there are many other options.

Link. Responsible for the physical transmission of data through the use of protocols such as Ethernet or WI-FI.

Network (Internet). This layer is where the IP address system is located and where routing is performed - the movement of packets between devices. The network layer combines the protocols: IP, ICMP, IGMP.

Transport layer. The TCP and UDP protocols are located here and are responsible for the transfer of data. The first carries out a guaranteed transfer of information, preliminarily establishing a connection to the network. The second sends messages without a "handshake", which increases the speed of data transfer, but also creates the risk of losing individual packets.

Applied. It combines all high level protocols that interact with system applications. These include Telnet, FTP, SMTP, SNMP, and the like.

Unique IP addresses that are assigned by special organizations (such as an ISP) are called external, white or public IP addresses. Public IP addresses are used to access the Internet and to communicate with other hosts over a public network. A device with an external IP address is visible to other users on the Internet.

There are also private IP addresses, also called gray or internal addresses. Gray IP addresses are assigned to devices on a local network and are not visible on the Internet. For example, you can imagine a house with several devices connected to a WI-FI router. They are all connected to the same network and have gray IP addresses.

The Internet began to grow rapidly from the 1980s, so there was a threat of depletion of the pool of possible addresses - they simply would not be enough for all networks and nodes. That's why in 1995, the IPv6 format was introduced. It increased the length of IP addresses from 32 to 128 bits, and changed the decimal system from hexadecimal.
IPv6 IP address consists of 16 octets (8 blocks of 2 octets), separated by colons. The full IPv6 notation looks like this: 2001:0bd7:0ccf:0006:0000:0000:012f:002d.
An IPv6 address can be compressed by excluding zeros from the entry. The abbreviated form of IPv6 is: 2001:bd7:ccf:12f:2d.

When surfing the Internet, a user establishes a connection through a browser to other servers based not primarily on the IP address, but rather on the domain name. The Domain Name System (DNS) serves to redirect the user to a permanent IP address for the final web resource. In simple terms, it converts the alphabetic values of a domain name into numbers for an IP address.

For example, you don't have to enter the numeric address "74.125.131.100" to get to a Google search engine site. It is enough to type in the address bar the domain name ".google.com".

DNS-server is responsible for such redirection, and it works according to information from DNS-records. Continuing the "telephone" analogy, if the IP address is a telephone number, the DNS server is a telephone book that contains all such numbers.

You can determine the IP address of the device you are using by using a browser search like "what is my IP". Many services, such as Whoer, 2ip, and WhiteWhois, check the IP address ID and provide more detailed information about the user (such as the name of the provider or the approximate location of the device).
On a local network, the address of the device is specified in the settings of the operating system, so you don't need to use external tools. You can determine the local IP address in the following ways.
Windows - through the command line (search -> "cmd" -> in the window type "ipconfig").
Unix/Linux - with the command "ifconfig".
MacOS - "System Preferences" -> "Network".
iOS - via "Settings. "Wi-Fi" -> click on the information icon "i" -> information in the tab "DHCP".
Android - "Settings" -> "About phone" -> "General information".
Anonymity and Security
"I'll identify you by IP."
This is more of a myth than a real threat. There is a misconception among users that an intruder can track a person by getting his external IP address. In fact, it's not that simple - customer information is safe with the provider. Only state security agencies can get access to this kind of personal data.The only thing you can find out from the IP address is the location of the ISP's equipment. And such information indicates only the approximate geolocation of the user, accurate to the country and city.

Using a TOR, proxy or VPN can protect you from the threats listed above. These types of protection hide the IP address, which anonymizes the user's online activity.The TOR network works on the principle of "onion routing," where user traffic is rerouted through multiple intermediary servers and out to the Internet. The user's public IP address changes constantly, which anonymizes activity and prevents traffic from being tracked. You can start using the TOR network by downloading the official Tor Browser, which, in addition to routing, blocks trackers of Internet resources.

Proxies and VPNs work in a similar way. Traffic is redirected through a server (or several servers) and goes to the Internet with an IP address substitution. VPN technology, unlike proxies, encrypts data on the way from the user to the intermediary server, so it is considered the best option in terms of security.

At the heart of the Internet and any IP/TCP network is IP addressing. Every system administrator should know its basics to build networks in both home and corporate environments.
It is also worth remembering about security, because a poorly configured network has vulnerabilities that can allow an intruder to disrupt connections or access personal information.